This invention is related to floating seat ring seals for valves. More specifically this invention is related to a seat ring construction for enclosing and mounting an O-ring between the seat ring and the seat ring recess in a gate valve.
It is quite well known in the art to provide floating seats in gate valves with an O-ring in the seat ring recess behind the seat ring to seal between the seat ring and the valve body. All of the prior art constructions require extremely fine tolerances and precise dimensioning in this area of the structure in order to establish a seal with a minimum of compression while at the same time sizing the seat assembly to prevent damage to the O-ring from over compression. In order for O-rings to be useful, effective sealing devises they must be resilient and be able to return to substantially their original shape. Once an O-ring is compressed so that stresses are raised above the elastic limit of the material, the O-ring will not return to its original cross-sectional shape, hence it will not function as a sealing device as originally intended it becomes marginal. Typically for any O-ring constructed of elastomeric material if it is squeezed or compressed such that its cross-sectional diameter is reduced more than approximately thirty (30) percent of the free cross-sectional diameter, then the O-ring will retain a permanent set and will not return to its original cross-sectional shape. This limitation on compression of the O-rings dictates very critical dimensions in gate valve seat ring construction so the O-rings can function both as seals and as springs and still return to substantially their original round cross-sectional shape. Because the dimensions are critical in this type of seat ring construction the tolerances for these dimensions are quite small. The machining and manufacture of these seat constructions are very expensive because of the precise, consistent accuracy required on the part of the machinist and the manufacturing size control of the O-ring. As a whole, this prior art seat ring construction is widely used in the valve industry, however, such is extremely expensive because of the precise machining which is required and the precise O-ring sizing which must be maintained in order for the seal design to function properly. The prior art seat construction briefly described here is shown in FIG. 2. of the drawings and such is described in detail in the following.